GMAT Sentence Correction (SC) | Re: Plural subject singular noun

I would say mobile phones is a collective noun, and we would therefore use an instrument in this case.

Instruments would be used if we were to say the following: "Mobile phones are one of many instruments used to spread political messages. Instruments is used in this sentence because we are alluding that there are multiple ways outside of mobile phones that we can spread messages.

Does this make sense?

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